1. Field of the Invention
The present invention relates to a novel metallic crosslinking coagent, particularly to a metallic crosslinking coagent for application to plastic material, preparation methods of the metallic crosslinking coagent, and a resin composition comprising the metallic crosslinking coagent.
2. Description of the Prior Arts
Nowadays, plastic materials are expected to provide good flame retardancy, mechanical property, thermal resistance, weather resistance, and safety to be widely used in various applications. To attain the flame retardancy, flame retardants, such as tetrabromobiphenyl A (TBBPA), polybrominated diphenylether (PBDE), polybrominated biphenyl (PBB), hexabromocyclododecane (HBCD), or polychloroalkane (for example, chlorinated paraffin (CP)), are typically added to the plastic materials to meet the flammability standards. However, due to safety concerns, the foresaid halogenated flame retardants are gradually prohibited or listed as controlled additives.
Researches are conducted to find a safer organic phosphorus flame retardant and inorganic flame retardant to replace the prohibited halogenated flame retardants. Nevertheless, organic phosphorus or inorganic flame retardants are usually incompatible and unstable in the low-polar rubber material, causing pollution, blooming or hydrolysis to the plastic product or mold made therefrom and thus deteriorating the physical properties of the plastic product.
To overcome the foregoing problems, an acrylate salt of metals represented by the following formula has been developed.

Wherein, M2+ is divalent metal ion, and R is hydrogen (—H) or methyl group (—CH3).
Common commercially available acrylate salts of metals include zinc diacrylate (ZDA), calcium diacrylate, zinc dimethacrylate (ZDMA), and fatty acid modified zinc diacrylate, their trade names include: Dymalink 633, Dymalink 634, Dymalink 705, and Dymalink 706 purchased from Cray Valley in France; K-CURE 339, K-CURE 439, K-CURE 633, and K-CURE 634 purchased from Kuo Ching Chemical Co., Ltd. in Taiwan; and ZN-DA 90 and ZN-DA 100 purchased from Nippon Shokubai Co. Ltd. The preparation methods and their applications are described in Taiwan Patent No. 530062, Japan Patent Application Publication No. S58-14416, Japan Patent Application Publication No. H4-10463, Japan Patent No. 4041175, Japan Patent No. 4286018, Japan Patent No. 4398157, U.S. Pat. No. 5,789,616, U.S. Pat. No. 6,278,010, and U.S. Pat. No. 7,217,829.
Said acrylate salts of metals can be used in a crosslinkable polymer composition and acts as a curing coagent. With the improvement of mechanical strength, stretching property, thermal resistance, wear resistance, solvent resistance, tensile strength, and adherence to metals, the acrylate salts of metals can be widely applied to the products of golf balls, rollers, sealing strips, cables, belts, and architectural materials.
As disclosed by Taiwan Patent No. 223652, Taiwan Patent No. 223095, European Patent Publication No. 0589701, Japan Patent Application Publication No. H2-158640, and Japan Patent Application Publication No. H6-256582, Sumitomo Chemical Co., Ltd. discloses a rubber composition for covering electric cables, which comprises (1) ethylene-α-olefin copolymer and/or ethylene-α-olefin-nonconjugated diene copolymer, (2) magnesium hydroxide and/or aluminum hydroxide, and (3) a zinc acrylate represented by the following formula:

Wherein, M is a divalent metal ion, R is hydrogen or a methyl group, m ranges from 1 and 2. The zinc acrylate can be used in the composition to maintain the elasticity, anti-scorch property and workability of the covering electric cables.
Mitsubishi Rayon Co., Ltd. discloses a metal salt of acrylic acid and propanoic acid in Japan Patent Application Publication No. 2000273366, the metal salt of acrylic acid and propanoic acid are represented by the following formula:

Wherein, M2+ is a divalent metal ion, and R is hydrogen or a methyl group. As the chemical structure implies, the metal salt of acrylic acid and propanoic acid also contains no organic phosphorus oxide group, but their fields of application are totally different from the plastic industry.
Furthermore, Sankyo Organic Chemicals Co., Ltd. discloses oxaphosphaphenanthrene oxide derivative salts in Japan Patent Application Publication No. S56-118441, which have a chemical structure represented by the following formula:

Wherein, M2+ is a divalent metal ion, and R is hydrogen or a methyl group. As shown above, the disclosed organic phosphorus metal salts do not contain an unsaturated carbon-carbon double bond for crosslinking. Further, the publication merely mentions that the organic phosphorus metal salts can be added in polyvinyl chloride and act as a stabilizer, but the organic phosphorus metal salts are incapable of increasing the crosslinking efficiency of the polyvinyl chloride.
To overcome the shortcomings, the present invention provides a novel metallic crosslinking coagent to mitigate or obviate the aforementioned problems.